Joe Polastre wrote:
To me, its a matter of defining abstractions clearly. Data link traditionally meant two points connected directly with the use of a physical wire (ie, it sits right above the "physical layer").
A minor but significant clarification, the data link in the IP world has traditionally meant two *or more* devices connected directly over a single shared-media. This is why so many protocols rely on link-local multicast and why LAN technologies that do not support it must emulate it, as we saw with LANE. It is also why we see some push from members in this working group for a "mesh-under" routing and forwarding strategy.
In this domain, we have this quirky ability to have multiple direct connections. For example, I may be able to directly connect with Kris, but I can also connect with Kris via John. From a software layering perspective, I can leverage both options at L2/L2.5 to make it look to the network layer like I have a reliable direct data-link connection to Kris, regardless of whether I reach Kris directly or talk to him via John. This becomes murkier if all of your "direct" connections are not direct at all or have no possible direct path--then you're potentially treading on the realm of L3 protocols. This is why this mesh networking domain has had the problem of communicating data and metadata between layers transparently, since each of the layers seems to muddle in other layers' business. I agree that MPLS is probably most applicable here, and really is one of these L2.5 services because it is abstracting all kinds of ugly mess underneath to look like a single data link to L3 protocols.
Putting MPLS' applicability to L2Ns aside, one thing to learn from MPLS is that the control protocols are, largely, IP protocols. Thus, MPLS is "route-over" but redefines the forwarding mechanisms to be below IP. But, yes, many claimed advantages of MPLS (e.g. label lookup, traffic engineering, etc.) may also see similar advantages in L2Ns.
-- Jonathan Hui [EMAIL PROTECTED] _______________________________________________ 6lowpan mailing list [email protected] https://www1.ietf.org/mailman/listinfo/6lowpan
